net: dsa: qca8k: add priority tweak to qca8337 switch

The port 5 of the qca8337 have some problem in flood condition. The
original legacy driver had some specific buffer and priority settings
for the different port suggested by the QCA switch team. Add this
missing settings to improve switch stability under load condition.
The packet priority tweak is only needed for the qca8337 switch and
other qca8k switch are not affected.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>